Active matrix backplanes are widely used in flat panel displays for routing signals to pixels of the display in order to produce viewable pictures. Presently, active matrix backplanes for flat panel displays are formed by performing a photolithography manufacturing process, which has been driven in the market by the demand for higher and higher resolution displays, which is not otherwise possible with other manufacturing processes. Photolithography is a pattern definition technique which uses electromagnetic radiation, such as ultraviolet (UV) radiation, to expose a layer of resist that is deposited on the surface of a substrate. Exemplary photolithography processing steps to produce an active matrix backplane include coat photoresist, pre-bake, soak, bake, align/expose, develop, rinse, bake, deposit layer, lift off photoresist, scrub/rinse, and dry. As can be seen, the active matrix backplane fabrication process includes numerous deposition and etching steps in order to define appropriate patterns of the backplane.
Because of the number of steps required to form an active matrix backplane with the photolithography manufacturing process, foundries of adequate capacity for volume production of backplanes are very expensive. An exemplary partial list of equipment needed for manufacturing active matrix backplanes includes glass-handling equipment, wet/dry strip equipment, glass cleaning equipment, wet clean equipment, plasma chemical vapor deposition (CVD) equipment, laser equipment, crystallization equipment, sputtering equipment, ion implant equipment, resist coater equipment, resist stripping equipment, developer equipment, particle inspection equipment, exposure systems, array filet/repair equipment, dry etch systems, anti-electrostatic discharge equipment, wet etch systems, and a clean oven. Furthermore, because of the nature of the active matrix backplane fabrication process, the foregoing equipment must be utilized in a class 1 or class 10 clean room. In addition, because of the amount of equipment needed and the size of each piece of equipment, the clean room must have a relatively large area, which can be relatively expensive.
Alternatively, a vapor deposition shadow mask process is well known and has been used for years in microelectronics manufacturing. The vapor deposition shadow mask process is a significantly less costly and less complex manufacturing process, compared to the photolithography process; however, the achievable resolution of, for example, an active matrix backplane formed via shadow mask technology, is limited. Today's shadow mask manufacturing techniques are limited to forming, for example, up to 80 pixels per inch, which is representative of, for example, a typical laptop display resolution. However, for small displays, such as in mobile phones and PDAs, a much higher resolution (up to 200 pixels per inch) is desired. Because of this demand for higher resolution, active matrix backplane manufacturers are migrating away from the less costly and less complex vapor deposition shadow mask process in favor of the photolithography process, but at the tradeoff of cost and complexity. Therefore, what is needed is a way to provide improved resolution that uses the more cost-effective vapor deposition shadow mask process and thereby extends its use in the manufacturing of flat panel displays.
Furthermore, in order to achieve improved resolution, the aperture size and spacing of the shadow mask is reduced accordingly. Therefore, the ability to maintain positional accuracy of the shadow mask in relation to the substrate during the deposition process becomes more and more critical to ensure proper placement of the electronic elements formed therewith. Because there are various heating effects that occur during a high-temperature deposition process, the ability to achieve small microelectronics dimensions and, thus, high resolution, by use of the vapor deposition shadow mask process is limited by thermal errors that play a considerable role in achieving positional accuracy. For example, the materials used for forming both the shadow mask and the substrate have an associated coefficient of thermal expansion (CTE). CTE is defined as the linear dimensional change of a material per unit change in temperature. A typical substrate material is anodized aluminum, which is aluminum atop which is grown a thin insulation layer. Aluminum has a CTE of 24 parts per million/degree Celsius (ppm/° C.). By contrast, typical materials used to form a shadow mask include nickel, stainless steel, and copper. Stainless steel has a CTE of 9.9–17.3 ppm/° C., copper has a CTE of 17 ppm/° C., and nickel has a CTE of 13.3 ppm/° C. Consequently, it is difficult to maintain proper registry between the two conjoined surfaces (i.e., the surface of the shadow mask in contact with the surface of the substrate), because of their differing CTEs, which results in different rates and amounts of expansion or contraction. This CTE mismatch creates geometric errors between the shadow mask and the substrate that are not tolerable.
Further, the radiant heat source used for vapor deposition produces hot spots and temperature gradients across the face of the shadow mask. As the shadow mask contains slots and holes, it does not come into uniform contact with the substrate to which it is mounted and, therefore it does not sink heat in a consistent way. As a result, thermal expansion can occur in the shadow mask relative to the substrate and thereby cause misregistration. To control this misregistration, specific locations on the shadow mask may need to be thermally regulated. By achieving a uniform temperature across the mask, uniform manufacture can take place. Accordingly, a need exists for a way to overcome the heating effects during a high-temperature deposition process and, thus, maintain positional accuracy of the shadow mask in relation to the substrate.
An exemplary system for fabricating an electronic device is described in U.S. Pat. No. 6,592,933, entitled “Process for Manufacturing Organic Electroluminescent Device.” The '933 patent describes a method for producing an organic electroluminescent device, which is formed of a first electrode formed on a substrate, a thin film layer on the first electrodes, the thin film layer formed of at least an emitting layer formed of an organic compound, a second electrode formed on the thin film layer, and a plurality of luminescent regions on the substrate. The method for producing the organic electroluminescent device forms spacers that have a height which exceeds a thickness of the thin film layer on the substrate and vapor-deposits a deposit while a mask portion of a shadow mask is kept in contact with the spacers. The shadow mask forms apertures that have reinforcing lines. Highly precise, fine patterning can be effected under wide vapor deposition conditions without degrading the properties of organic electroluminescent elements, and high stability can be achieved by the method without limiting the structure of the electroluminescent device. While the '933 patent provides a suitable system for fabricating an electronic device, it does not address ways to overcome the heating effects that cause misregistration between the shadow mask and the substrate during a high-temperature deposition process. Therefore, the production system described in the '933 patent does not minimize temperature gradients across a shadow mask and substrate. Further, the invention of the '933 patent does not ensure negligible relative movement between the shadow mask and the substrate during any of the critical deposition stages of the manufacturing process and, therefore, does not extend the use of the vapor deposition shadow mask process for manufacturing high-resolution displays.
It is therefore an object of the invention to manufacture, for example, a flat panel display with improved resolution using the more cost-effective vapor deposition shadow mask process.
It is another object of this invention to overcome the heating effects that occur during a high-temperature deposition process and, thus, maintain positional accuracy of a shadow mask in relation to the substrate.
It is yet another object of this invention to provide a temperature measurement and cooling system to provide thermal regulation and minimize temperature gradients across a shadow mask and substrate.
It is yet another object of this invention to ensure negligible relative movement between the shadow mask and the substrate during any of the critical deposition stages of the manufacturing process.